How to define an array with fractional index number in MATLAB?

How to define an array with fractional index number in MATLAB?

[José-Luis]

Are you talking about interpolation? If not, what do you mean?

[Udit Srivastava]

Like suppose that I need to create a function named pressure denoted by 'p' (a 2-D matrix) which depends on 2 variables 'r' and 'z'.

'u', 'v', 'w' are linear matrices which also depend on 2 variables 'r' and 'z'.

'r' and 'z' are linear matrix defined below take i={1,2,3,4,5,6,7,8,9,10}

r(i)=i/10

z(i)=i/10

u(i) = 2*r(i) + 3*z(i)

v(i) = 8*r(i) + 4*z(i)

w(i) = 3*r(i) + 2*z(i)

p = p(r,z), which is given as,

p(r(i),z(j)) = 2*v(i) - 4*u(i) + w(j)

Now suppose value of 'p' at a given location (r,z) say (0.4,0.8) is needed, I want that if I give the input p(0.4,0.8), I get the result.

[Adam]

Isn't this exactly the purpose of a function rather than an array?

[José-Luis]

My thought exactly.

Use a function of two variables.

[Udit Srivastava]

basically, i have to define an array with fractional index like p(r(i),z(j))

Answer 1

[KSSV]

You cannot define fractional indices in any software.......fortran, c takes from 0 to n...where as matlab takes from 1 to n. May be you want to call a fractional array; you have to follow like this.

x = rand(10,1) ;
n = length(x) ;
for i = 1:n
    x(i)
end

Answer 2

[Adam]

'have to' for what purpose?

Use

doc containers.Map

if you want to set up a finite lookup table of results to index into without using integer lookups.

But if your code is sufficiently fast then a function works fine and recalculate whatever is asked for.